1. Field of the Invention
The invention relates to an electrically insulated switching element driver that transmits power and signals from a primary side to a secondary side, via a pulse transformer, and that drives a switching element on the basis of signals transmitted to the secondary side, and relates also to a method for controlling the electrically insulated switching element driver.
2. Description of the Related Art
Japanese Patent Application Publication No. 7-307653 (JP-A-7-307653) discloses a switching element driving circuit provided with a control circuit that generates a control signal made up of pulses whose duty ratio is controlled; a frequency dividing circuit that outputs first and second control signals; a first driving circuit that generates a first driving signal, the first driving circuit being made up of a pulse transformer and a clamp circuit that clamps the back emf voltage generated by the pulse transformer; a second driving circuit that generates a second driving signal, the second driving circuit being made up of a pulse transformer and a clamp circuit that clamps the back emf voltage generated by the pulse transformer; and a synthesizing circuit that generates a driving signal that drives a switching element. In the above switching element driving circuit, the frequency dividing circuit divides the frequency of the control signal and outputs a first control signal in which a high level period and a low level period are arranged, and a second control signal in which a high level period is arranged during the low level period of the first control signal and a low level period is arranged during the high level period of the first control signal. The first driving circuit generates a first driving signal by operating in synchrony with the first control signal, and the second driving circuit generates a second driving signal by operating in synchrony with the second control signal, where a high level period is arranged during the low level period of the first driving signal and a low level period is arranged during the high level period of the first driving signal. The synthesizing circuit generates the above-described driving signal by combining the first driving signal and the second driving signal.
In the above switching element driving circuit, however, a driving signal for driving the switching element is transmitted via a pulse transformer, and is not necessarily be an exact square wave. Therefore, the driving signal may not be transmitted properly.